1. Field of the Invention
The present invention relates generally to a mobile communication system, and more particularly to a method of selecting a base transceiver system in a communication system that is for a mobile station to request a forward data transmission.
2. Background of the Related Art
As is well known, a mobile communication system based on a code division multiple access (CDMA) divides a space into cells and sectors. Each mobile station registers a sector where it receives a signal having the best receiving strength among received signals to perform signal transmission and reception.
Up to the present, the mobile radio communication has been designed for the purpose of providing real-time voice services such as IS-95. Accordingly, the mobile communication system for providing the real-time voice services has been designed to make each mobile station observe the minimum transmission quality, i.e., signal strength, over a threshold value in a cell area.
To cope with neighboring areas between two cells where the signal from a base station of a cell become weak, a soft handover technique using a macro diversity has been proposed and used.
Meanwhile, with the recent increase of data service requests through the Internet, the standard such as HDR (high data rate, Qualcomm), 1xTREME (Motorola, Nokia), etc., has been proposed.
According to the standard proposed in the system, the mobile station detects signal of sectors which are determined to be active sets, and reports a useable transmission rate to the sector having the most superior channel environment. The respective sector schedules packets to be transmitted to the respective mobile station accordingly, and transmits the packets using an adaptive modulation technique through a down channel. This can achieve the performance improvement in the voice communication since respective selected diversities are used instead of performing the soft handover using all radio resources of the two cells.
The above-described HDR system has been proposed to provide only a high-speed radio packet data service.
This system implements the high-speed radio Internet technique based on the Internet protocol, and especially can easily implement a radio Internet environment by connecting HDR equipment to the existing CDMA network. Also, it supports both voice and data in the same network by separately optimizing voice and data spectrums.
Especially, in transmitting data to an up link (i.e., from the mobile station to the base transceiver system), the HDR system basically has the same structure as IS-95, IS-2000, and WCDMA systems, and in transmitting data to a down link (i.e., from the base transceiver system to the mobile station), it commonly accesses the radio resources (i.e., common channels) according to an asynchronous TDM method.
Accordingly, in the down-link access, the respective mobile station periodically reports the channel state to the base transceiver system through the best signal of one among the active sets, and the base transceiver system schedules the time point and sector where the data is transmitted, and selects an encoder that supports the transmission rate required by the mobile station to transmit the data to the mobile station.
For example, as shown in FIG. 1, in the mobile communication system including at least one base transceiver system (BTS) whose regions BTSA, BTSB, and BTSC are divided into several sectors A1˜A3, B1˜B3, and C1˜C3, respectively, and a base station controller (BSC) for managing the base transceiver system (BTS), a certain mobile station located in a superimposing region of the sectors A2 and B1 (which is subject to handover) forms one active set that receives a pilot signal from the sectors A2 and B1.
Here, the mobile station calculates the channel state of the respective base transceiver systems (or sectors) using the pilot signals from the respective base transceiver systems (or sectors) in the active set or signals that provide the same function, calculates the transmission rate suitable for a bit error rate or packet error rate based on the channel state, and requests the data transmission to the corresponding base transceiver system (or sector) that can transmit at the highest transmission rate.
Accordingly, the mobile station requests the forward data transmission to the sector having a better channel environment than the other sector between the sectors A2 and B1.
This forward data transmission request of the mobile station to the base transceiver system (or sector) is performed using a data rate control (DRC) media access control channel of the up link, and the request for the transmission rate is reported through the transmission of the request to the base transceiver system (or sector) covering a Walsh.
This DRC transmission is performed during a DRCLength slot defined by a system parameter, and the base transceiver system (or sector) discriminates the respective mobile stations using the covered Walsh code.
As described above, according to the conventional system, the data transmission is requested to the base transceiver system (or sector) at the data transmission rate in proportion to the channel environment of the base transceiver system (or sector).
In the general mobile radio communication system as described above, the number of mobile stations which have the respective base transceiver systems (or sectors) as their active sets is variable, and is generally independent of the channel state.
Also, according to the conventional system, the respective mobile station does not have information on the number of mobile stations in the base transceiver system (or sector) and the load extent, and thus the respective mobile station requests the forward data transmission to the base transceiver system (or sector) having the best channel environment irrespective of the load extent of the base transceiver system (or sector).
As a result, even though the corresponding base transceiver system to which the respective mobile station requests the data transmission has a good channel environment, the amount of data actually transmitted to the mobile station is reduced if all the mobile stations managed by the base station have excessive loads.